Valganciclovir

Esterase-Mediated Hydrolysis in Intestinal and Hepatic Systems

After oral administration, this compound is rapidly and extensively metabolized into ganciclovir. roche-hiv.com This biotransformation is facilitated by esterase enzymes present in the intestinal wall and the liver. fda.govroche-hiv.comdrugbank.compmda.go.jp These enzymes hydrolyze the L-valyl ester bond, releasing the active ganciclovir and the amino acid valine. wikipedia.orgoatext.com This process is so efficient that systemic exposure to the prodrug, this compound, is transient and low. pmda.go.jptga.gov.au

Kinetics of this compound Conversion to Ganciclovir

The conversion of this compound to ganciclovir is a rapid process. Following oral administration, this compound is quickly absorbed, and peak plasma concentrations of ganciclovir are typically observed within 1 to 3 hours. fda.govnih.gov The systemic exposure to this compound itself is minimal, with its area under the concentration-time curve (AUC) being approximately 1% to 3% of that of ganciclovir. pmda.go.jptga.gov.au The half-life of ganciclovir after oral administration of this compound is approximately 4.1 hours in individuals who are HIV- and CMV-seropositive. roche-hiv.com

Significance of the L-Valyl Ester Moiety in Enhancing Intestinal Absorption

The addition of the L-valyl ester to ganciclovir significantly improves its oral bioavailability. ijpsjournal.comnih.gov The bioavailability of ganciclovir from oral this compound is approximately 60%, which is about 10 times higher than that of oral ganciclovir capsules. ijpsjournal.comnih.gov This enhanced absorption is attributed to the L-valyl ester moiety, which allows the prodrug to be recognized and transported by the peptide transporter PEPT1 in the intestine. oatext.comijpsjournal.comresearchgate.net This transport mechanism facilitates more efficient absorption of the drug from the gastrointestinal tract. oatext.comijpsjournal.com

Initial Phosphorylation by Viral Protein Kinases (e.g., pUL97 in Human Cytomegalovirus)

The initial and crucial step in the activation of ganciclovir within a human cytomegalovirus (HCMV)-infected cell is its phosphorylation to ganciclovir monophosphate. fda.govpatsnap.com This reaction is catalyzed by a viral protein kinase encoded by the HCMV UL97 gene, known as pUL97. fda.govasm.orgscispace.com This initial phosphorylation is highly selective for virus-infected cells because the pUL97 kinase is only present in these cells. drugbank.compatsnap.com This selectivity is a key factor in the targeted action of the drug. patsnap.com The pUL97 kinase is essential for the antiviral activity of ganciclovir, and mutations in the UL97 gene can lead to ganciclovir resistance. asm.org

Subsequent Phosphorylation by Cellular Kinases to Diphosphate and Triphosphate Forms

Following the initial phosphorylation by the viral kinase, cellular kinases take over to complete the activation process. fda.govdrugbank.comwikipedia.org Cellular enzymes, such as guanylate kinase and phosphoglycerate kinase, further phosphorylate ganciclovir monophosphate to ganciclovir diphosphate and then to the active form, ganciclovir triphosphate. wikipedia.orgaksci.com Ganciclovir triphosphate is the ultimate active metabolite that inhibits viral DNA synthesis. drugbank.comnih.govpatsnap.com This active form accumulates in CMV-infected cells at concentrations that are significantly higher than in uninfected cells, further enhancing the drug's specificity. wikipedia.org

Table 1: Key Pharmacokinetic Parameters of this compound and Ganciclovir

Table 2: Enzymes Involved in this compound Activation

Intracellular Accumulation and Prolonged Half-Life of Ganciclovir Triphosphate (GCV-TP)

A critical feature of ganciclovir's effectiveness is the preferential accumulation and prolonged persistence of its active triphosphate metabolite, GCV-TP, within virus-infected cells. nih.govoup.com The initial and rate-limiting step of phosphorylation to ganciclovir monophosphate is catalyzed by a viral-encoded protein kinase, UL97 in CMV-infected cells. patsnap.comuonbi.ac.kenih.gov Subsequently, cellular kinases convert the monophosphate to diphosphate and then to the active GCV-TP. nih.govnih.govwikipedia.org

This reliance on a viral kinase for the initial phosphorylation step leads to a significantly higher concentration of GCV-TP in infected cells compared to uninfected cells, where phosphorylation is minimal. wikipedia.orgtorso.co.inxn--80aabqbqbnift4db.xn--p1ai Studies have shown that GCV-TP levels can be 10-fold greater in CMV-infected cells. nih.govwikipedia.orgxn--80aabqbqbnift4db.xn--p1ai

Furthermore, GCV-TP exhibits a remarkably long intracellular half-life. Once formed, it is slowly metabolized, persisting in infected cells for an extended period. fda.goveuropa.eu Reported intracellular half-life values for GCV-TP range from 16.5 to 24 hours. nih.goveuropa.eubasicmedicalkey.com One study noted a half-life of 18 hours after the removal of extracellular ganciclovir. fda.gov Another study in HCMV-infected cells determined the half-life of GCV-TP to be approximately 48.2 hours. nih.gov This prolonged intracellular presence ensures sustained inhibition of viral replication long after the extracellular drug has been cleared. basicmedicalkey.com

Competitive Antagonism with Deoxyguanosine Triphosphate (dGTP)

Structurally, GCV-TP is an analog of the natural nucleotide deoxyguanosine triphosphate (dGTP). patsnap.compharmgkb.org This structural similarity allows it to act as a competitive inhibitor of viral DNA polymerase. patsnap.comeuropa.eunih.gov GCV-TP competes with the endogenous dGTP for the active site of the viral DNA polymerase. oup.comuonbi.ac.ketoku-e.com By binding to the polymerase, GCV-TP effectively reduces the incorporation of the natural nucleotide required for viral DNA elongation.

Substrate Properties for Viral DNA Polymerase

In addition to being a competitive inhibitor, GCV-TP also serves as a substrate for the viral DNA polymerase. sierrabioresearch.compharmgkb.orgnih.gov The viral enzyme recognizes GCV-TP and incorporates it into the growing viral DNA strand in place of dGTP. oup.comsierrabioresearch.compharmgkb.org This incorporation is a crucial step in its mechanism of action. sierrabioresearch.com

Mechanism of Viral DNA Chain Termination

Although ganciclovir possesses a 3'-hydroxyl group equivalent, its incorporation into the viral DNA chain ultimately leads to the cessation of DNA elongation. wikipedia.orgsierrabioresearch.comnih.gov The incorporation of GCV-TP destabilizes the DNA strand and prevents the formation of phosphodiester bridges, which are necessary for continued DNA synthesis. drugbank.com This results in the premature termination of the viral DNA chain, effectively halting viral replication. patsnap.cominvivogen.com Some research suggests that termination may be delayed, occurring after the incorporation of one additional nucleotide following the ganciclovir analog. nih.govnih.gov

Impact of Food on this compound Absorption and Ganciclovir Bioavailability

The administration of this compound with food significantly enhances its absorption, leading to greater systemic exposure to the active moiety, ganciclovir. jscimedcentral.com Studies have demonstrated that taking this compound with a meal increases the bioavailability of ganciclovir. medsafe.govt.nzjscimedcentral.com

One study involving HIV-positive subjects found that administration of this compound with a high-fat meal resulted in a 30% increase in the steady-state area under the curve (AUC) for ganciclovir. fda.gov Another source indicates that food can increase the bioavailability of this compound by approximately 25%. jscimedcentral.com Consequently, administration with food is recommended to optimize drug exposure. medsafe.govt.nzhres.catga.gov.au Dose proportionality for ganciclovir AUC has been demonstrated only under fed conditions. hres.cafda.govfda.gov

Role of Peptide-Mediated Active Transport in Intestinal Uptake

The enhanced intestinal absorption of this compound compared to ganciclovir is attributed to its recognition and transport by specific carrier proteins in the gut. researchgate.net The L-valine ester modification allows this compound to be recognized as a substrate by the human intestinal peptide transporter 1 (PEPT1). researchgate.netnih.gov PEPT1 is a high-capacity, low-affinity transporter primarily expressed on the apical membrane of intestinal enterocytes, responsible for the absorption of dietary di- and tripeptides. guidetopharmacology.org

By mimicking the structure of a peptide, this compound utilizes this active transport mechanism to facilitate its uptake from the intestinal lumen. researchgate.netcapes.gov.br In contrast, the parent drug, ganciclovir, is not a substrate for PEPT1 and is poorly absorbed. researchgate.netnih.gov Studies have shown that this compound competitively inhibits PEPT1-mediated transport. researchgate.netnih.gov In addition to the intestinal transporter PEPT1, this compound is also recognized by the renal peptide transporter PEPT2 with high affinity. researchgate.netnih.gov

Bioavailability Enhancement of Ganciclovir via this compound Prodrug Strategy

The development of this compound as a prodrug represents a successful strategy to overcome the poor oral bioavailability of ganciclovir. nih.gov Oral ganciclovir has a very low bioavailability, estimated to be between 5% and 9%. jscimedcentral.comdrugbank.com

The this compound prodrug strategy dramatically improves this pharmacokinetic limitation. Following oral administration with food, the absolute bioavailability of ganciclovir from this compound tablets is approximately 60%. hres.cafda.govfda.govtga.gov.audrugbank.com This represents a roughly 10-fold increase in bioavailability compared to oral ganciclovir capsules, allowing for effective systemic concentrations of ganciclovir to be achieved with oral dosing. medsafe.govt.nznih.gov

Extent of Plasma Protein Binding

Due to the rapid and extensive conversion of this compound to ganciclovir, the plasma protein binding of this compound itself has not been determined. fda.govroche.com The active moiety, ganciclovir, exhibits very low binding to plasma proteins. pharmgkb.org The plasma protein binding of ganciclovir is only 1% to 2% over a concentration range of 0.5 to 51 µg/mL. fda.govdrugbank.comnih.goveuropa.eu This low level of protein binding means that drug interactions involving displacement from binding sites are not anticipated. roche.com

Non-Clinical Tissue Distribution Studies

Non-clinical studies in animal models have shown that the tissue distribution pattern following administration of this compound is essentially the same as that of ganciclovir. pmda.go.jp The drug distributes to all well-perfused organs and tissues. pmda.go.jp The steady-state volume of distribution for intravenously administered ganciclovir is approximately 0.7 L/kg. fda.goveuropa.eu In non-clinical safety studies, the primary target organs for toxicity for both this compound and ganciclovir were identified as the reproductive, hematopoietic, renal, and gastrointestinal systems. pmda.go.jpcbg-meb.nl The highest concentrations of the drug were found in the kidneys, which is consistent with its primary route of elimination. pmda.go.jp

Permeability Across Biological Barriers (e.g., Blood-Brain Barrier)

The ability of a drug to cross the blood-brain barrier (BBB) is critical for treating central nervous system (CNS) infections. Non-clinical studies in rats have shown that after administration of radiolabelled this compound and ganciclovir, there is low exposure of the central nervous system to both compounds. cbg-meb.nl The BBB's tight junctions between vascular endothelial cells typically restrict the passage of larger molecules (over 500 Da) and most small molecules. uu.nl

Distribution studies in rats using intravenously administered radiolabelled this compound and ganciclovir demonstrated rapid distribution to various tissues, with exposure in tissues like the kidneys and liver exceeding that in whole blood. cbg-meb.nl However, CNS penetration was limited for both compounds. cbg-meb.nl This restricted access is a key consideration in CNS therapeutics. The brain penetration of drugs is also influenced by active efflux transporters like P-glycoprotein (P-gp), which actively pump substances out of the brain. nih.gov While specific studies on this compound as a P-gp substrate are not detailed, this mechanism is a known factor in limiting CNS drug concentrations. nih.gov

Interspecies Metabolic Comparisons (e.g., mice, rats, dogs, monkeys)

Identification of Major Excreted Metabolites

This compound undergoes rapid and extensive conversion to its active form, ganciclovir, primarily through the action of esterases in the intestinal wall and liver. Following this initial hydrolysis, ganciclovir is the principal and essentially the only significant metabolite detected systemically. pmda.go.jptga.gov.au Non-clinical and clinical studies consistently report that ganciclovir is the major compound excreted, predominantly via the kidneys. tga.gov.auhres.ca

Investigations using radiolabeled ganciclovir have shown that no other metabolites account for more than 1% to 2% of the radioactivity recovered in urine or feces. tga.gov.auhres.ca This indicates that after the initial conversion from the prodrug, ganciclovir itself is not significantly metabolized further before elimination. The primary route of elimination is renal excretion of unchanged ganciclovir through a combination of glomerular filtration and active tubular secretion. tga.gov.auasm.org

Mechanistic Understanding of Elimination Half-Life Variations

The elimination half-life of ganciclovir, following the administration of this compound, is subject to significant variation, primarily influenced by renal function. In individuals with normal renal function, the terminal half-life of ganciclovir is approximately 4.08 hours. However, this can be considerably extended in patients with impaired renal function. nih.gov

The mechanism behind this variation lies in the primary route of ganciclovir elimination. Since over 90% of ganciclovir is cleared unchanged by the kidneys, any impairment in renal function directly impacts its removal from the body. Ganciclovir clearance demonstrates a strong correlation with creatinine clearance. nih.govresearchgate.net In cases of severe renal impairment and end-stage renal disease, the elimination half-life of ganciclovir can be dramatically prolonged, reaching up to 68.1 hours. nih.gov

Furthermore, factors that interfere with renal tubular secretion can also affect ganciclovir's half-life. For instance, co-administration of drugs like probenecid, which competes for renal tubular excretion, can decrease the renal clearance of ganciclovir, leading to increased exposure and a prolonged half-life. tga.gov.aumedsafe.govt.nz

The intracellular half-life of the active moiety, ganciclovir triphosphate, is also a critical factor in its antiviral effect. Within cytomegalovirus (CMV)-infected cells, ganciclovir triphosphate has a prolonged half-life of 18 hours, which is significantly longer than the plasma half-life of ganciclovir. tga.gov.auroche.com This intracellular persistence allows for sustained inhibition of viral DNA synthesis. tga.gov.au

Influence of Renal Impairment on Ganciclovir Exposure

Renal impairment profoundly influences the exposure to ganciclovir following the administration of this compound. Decreased renal function leads to reduced clearance of ganciclovir, resulting in a corresponding increase in systemic exposure (AUC) and maximum plasma concentrations (Cmax). tga.gov.aunih.gov

Studies have demonstrated a direct relationship between the degree of renal impairment and the extent of increased ganciclovir exposure. In patients with severe renal impairment, ganciclovir concentrations were significantly higher (Cmax of 8.5 µg/mL versus 5.8 µg/mL in healthy subjects) and the time to reach maximum concentration (Tmax) was delayed (4.3 hours versus 2.0 hours). nih.govresearchgate.net This elevated and sustained exposure necessitates dosage adjustments in patients with compromised renal function to avoid potential toxicities. tga.gov.auhres.canih.govmedsafe.govt.nz

The following table summarizes the impact of renal impairment on key pharmacokinetic parameters of ganciclovir after this compound administration.

Data compiled from a study involving oral administration of 900 mg of this compound. nih.gov

Non-Linear Pharmacokinetics Considerations

The pharmacokinetics of this compound, with respect to the resulting ganciclovir exposure, are generally considered to be linear with respect to dose under fed conditions. pmda.go.jp However, dose proportionality has been demonstrated to be dependent on administration with food. tga.gov.aumedsafe.govt.nz

Non-linear mixed-effects modeling (NONMEM) has been utilized to describe the pharmacokinetics of ganciclovir derived from both oral this compound and oral ganciclovir. researchgate.net These models often employ a two-compartment structure with first-order absorption and elimination to characterize the concentration-time data. asm.orgresearchgate.netnih.gov Such models have been instrumental in understanding the variability in ganciclovir pharmacokinetics among different patient populations. While the fundamental disposition of ganciclovir is linear, factors such as renal function introduce significant variability that can be perceived as non-linearity in the dose-exposure relationship across a diverse population.

Comparative Pharmacokinetic Profiles of this compound and Ganciclovir

The primary pharmacokinetic advantage of this compound over oral ganciclovir is its significantly improved bioavailability. The bioavailability of ganciclovir from this compound is approximately 60%, which is about 10 times greater than that from oral ganciclovir capsules. pmda.go.jp

This enhanced bioavailability translates into a more favorable pharmacokinetic profile for achieving therapeutic ganciclovir concentrations. Systemic exposure to ganciclovir (AUC) is substantially higher following oral administration of this compound compared to oral ganciclovir. For instance, a 900 mg once-daily dose of this compound results in a ganciclovir AUC comparable to that achieved with a standard intravenous dose of ganciclovir. researchgate.net In solid organ transplant recipients, the daily AUC for ganciclovir from this compound (900 mg once daily) was 46.3 ± 15.2 µg·h/mL, compared to 28.0 ± 10.9 µg·h/mL from oral ganciclovir (1000 mg three times daily). medsafe.govt.nz

The following table provides a comparative overview of key pharmacokinetic parameters for ganciclovir following administration of this compound and oral ganciclovir in solid organ transplant patients.

Data from a study in solid organ transplant patients. medsafe.govt.nz

Due to its rapid conversion, systemic exposure to the prodrug, this compound, is low and transient. pmda.go.jp The AUC and Cmax of this compound are approximately 1% and 3% of those of ganciclovir, respectively. tga.gov.au Non-clinical studies in various animal species have confirmed the rapid hydrolysis of this compound to ganciclovir, with short half-lives for the prodrug, ranging from 5 minutes in mice to 30 minutes in dogs and cynomolgus monkeys. pmda.go.jp

High-Performance Liquid Chromatography (HPLC) Development

The development of HPLC methods for this compound is crucial for quality control and ensuring the efficacy of pharmaceutical products. wisdomlib.org These methods are validated according to guidelines from the International Conference on Harmonisation (ICH) to ensure accuracy, precision, and reliability. wisdomlib.orgwisdomlib.org

Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) is a predominant technique for the analysis of this compound. globalresearchonline.net This is due to the non-polar nature of the drug, which makes it well-suited for separation on a non-polar stationary phase with a polar mobile phase. wisdomlib.org

Several RP-HPLC methods have been developed for the determination of this compound in bulk drug and tablet dosage forms. wisdomlib.orgjidps.com These methods are designed to be simple, selective, linear, precise, and accurate. wisdomlib.org A common stationary phase used is a C18 column. scispace.comjpionline.org The mobile phase composition is a critical parameter that is optimized to achieve good separation. For instance, a mixture of methanol and water (45:55% v/v) has been used, resulting in a retention time of approximately 2.38 minutes. jidps.com Another method utilized a mobile phase of acetonitrile and potassium dihydrogen phosphate buffer (pH 4.5) in a 55:45% v/v ratio. wisdomlib.org The detection of this compound is typically carried out using a UV detector, with a common wavelength being 254 nm. wisdomlib.orgscispace.comjpionline.orgijnrd.org

The table below summarizes the conditions of various developed RP-HPLC methods for this compound analysis.

Stability-indicating assay methods are crucial for monitoring the degradation of a drug substance over time and under various stress conditions. rroij.com For this compound, which is susceptible to degradation in aqueous solutions, developing such methods is particularly important. rroij.com These methods must be able to separate the intact drug from its degradation products, ensuring that the quantification of the active pharmaceutical ingredient is not affected by the presence of impurities. ejpmr.com

Forced degradation studies are performed to demonstrate the stability-indicating nature of an analytical method. ejpmr.com this compound is subjected to stress conditions such as acid and base hydrolysis, oxidation, photolysis, and thermal degradation. rroij.comejpmr.com It has been observed that this compound is particularly susceptible to degradation under basic hydrolysis and oxidation. rroij.comscholarscentral.com For instance, significant degradation (95-100%) was observed in basic conditions and with 30% hydrogen peroxide. rroij.com In contrast, the drug shows milder degradation in acidic and neutral conditions and is relatively stable to photolysis. rroij.comscholarscentral.com

The developed stability-indicating RP-HPLC methods can effectively separate this compound from its degradation products. rroij.comejpmr.com For example, a method using a Hibar C18 column and a mobile phase of methanol and 25mM ammonium acetate (pH 3.0) was able to resolve the drug from degradants formed under various stress conditions. rroij.com Another method using a Phenomenex Gemini C18 column with a mobile phase of 0.01M sodium dihydrogen phosphate buffer (pH 5.0) and acetonitrile also demonstrated good separation of the drug from its degradation products. ejpmr.com

The table below outlines the degradation of this compound under different stress conditions as reported in a stability-indicating method study.

In HPLC, the elution technique, which is the process of passing the mobile phase through the column to move the analytes, can be either isocratic or gradient. danaher.commastelf.com

Isocratic elution employs a constant mobile phase composition throughout the analysis. danaher.commastelf.com This method is valued for its simplicity, reproducibility, and cost-effectiveness, making it suitable for routine analysis of simple mixtures. danaher.comuhplcs.com Several isocratic RP-HPLC methods have been successfully developed for the determination of this compound. wisdomlib.orgijnrd.orgrroij.com These methods offer the advantage of straightforward operation and stable baselines. danaher.com

Gradient elution , on the other hand, involves changing the mobile phase composition during the separation process. globalresearchonline.netmastelf.com This technique is particularly useful for analyzing complex samples containing analytes with a wide range of polarities. danaher.com By gradually increasing the solvent strength, gradient elution can improve peak resolution and reduce analysis time for complex mixtures. mastelf.com A gradient HPLC method was used for impurity profiling of this compound hydrochloride using a mobile phase of methanol and trifluoroacetic acid. actascientific.com

The choice between isocratic and gradient elution depends on the complexity of the sample and the analytical goal. danaher.com For routine quality control of this compound in pharmaceutical formulations, where the sample is relatively simple, isocratic methods are often preferred due to their simplicity and robustness. wisdomlib.orguhplcs.com However, for analyzing complex mixtures, such as identifying degradation products or impurities, gradient elution provides better separation efficiency. danaher.com

Stability-Indicating Methods for Degradation Products

Liquid Chromatography-Mass Spectrometry (LC-MS/MS)

Liquid Chromatography-Mass Spectrometry (LC-MS/MS) is a powerful and highly sensitive analytical technique that combines the separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry. pharmjournal.ru This technique is particularly valuable for the analysis of drugs and their metabolites in biological matrices due to its high selectivity and sensitivity. pharmjournal.ru

This compound is a prodrug that is rapidly converted to its active metabolite, ganciclovir, in the body. pharmjournal.ru Therefore, it is often necessary to simultaneously quantify both this compound and ganciclovir in biological fluids like human plasma for pharmacokinetic studies. actascientific.compharmjournal.ru LC-MS/MS is the method of choice for this purpose. actascientific.com

Several LC-MS/MS methods have been developed and validated for the simultaneous determination of this compound and ganciclovir in human plasma. actascientific.compharmjournal.runih.gov These methods typically involve a sample preparation step, such as protein precipitation or solid-phase extraction, to remove interferences from the plasma matrix. nih.gov The separation is then performed on a reversed-phase column, followed by detection using tandem mass spectrometry in the multiple reaction monitoring (MRM) mode, which provides high selectivity and sensitivity. nih.gov

For example, one method utilized a linear gradient mobile phase of 0.02% formic acid and methanol with an Aquasil C18 column for separation. researchgate.net Another method employed a mobile phase of water, trifluoroacetic acid, and methanol with a Chromolith RP18e column. nih.gov The linearity of these methods has been established over a range of concentrations, for instance, 5-800 ng/mL for this compound and 70-11,200 ng/mL for ganciclovir in one study. nih.gov Another study reported a linearity range of 5-1,000 ng/mL for this compound and 50-10,000 ng/mL for ganciclovir. pharmjournal.rushimadzu-webapp.eu

The table below details the parameters of a validated LC-MS/MS method for the simultaneous quantification of this compound and ganciclovir.

Use of Internal Standards and Matrix Effect Compensation

In bioanalytical methods, particularly those employing liquid chromatography-tandem mass spectrometry (LC-MS/MS), the use of internal standards (IS) is crucial for accurate quantification. nih.govslideshare.net The matrix effect, a phenomenon where components in a biological sample interfere with the ionization of the analyte, can lead to signal suppression or enhancement, thereby affecting the accuracy and precision of the results. slideshare.net

To compensate for these matrix effects, a suitable internal standard is co-administered with the sample. Ideally, a stable isotope-labeled internal standard (SIL-IS) is the preferred choice as it co-elutes with the analyte and experiences similar matrix effects. slideshare.net For this compound analysis, five-fold deuterated ganciclovir (GCV-d5) and this compound (VGC-d5) have been successfully used as internal standards. nih.govdaneshyari.com These deuterated standards effectively compensate for matrix effects in human and rat plasma, ensuring the reliability of the quantification. nih.gov

Strategies to minimize matrix effects also include optimizing sample extraction procedures and chromatographic conditions. slideshare.net Protein precipitation followed by hydrophilic interaction liquid chromatography (HILIC) is one such approach that has been employed for the analysis of this compound and its active metabolite, ganciclovir, in plasma. nih.govdaneshyari.com

Ultraviolet (UV) Spectrophotometry for Bulk and Formulations

UV spectrophotometry offers a simple, economical, and rapid method for the quantification of this compound in bulk drug and pharmaceutical formulations. ijcpa.inresearchgate.netamazonaws.com This technique is based on the principle that the drug absorbs UV radiation at a specific wavelength.

Several studies have developed and validated UV spectrophotometric methods for this compound. The wavelength of maximum absorbance (λmax) for this compound has been reported at various wavelengths depending on the solvent used. For instance, in methanol, the λmax is observed at 254 nm. researchgate.netresearchgate.net In distilled water, the maximum absorbance is at 252 nm, with the area under the curve measured between 247 nm and 257 nm. ijcpa.in When 0.1N HCl is used as the solvent, the λmax is found to be 250 nm. amazonaws.com

These methods have been validated according to International Council for Harmonisation (ICH) guidelines and have demonstrated good linearity, accuracy, and precision, making them suitable for routine quality control analysis of this compound in its dosage forms. ijcpa.inamazonaws.com

Table 1: UV Spectrophotometric Methods for this compound

Specificity and Selectivity

Specificity is the ability of an analytical method to assess unequivocally the analyte in the presence of components that may be expected to be present, such as impurities, degradation products, and matrix components. rroij.comresearchgate.net In the context of this compound analysis, this means the method should be able to distinguish and quantify this compound without interference from its diastereomers, degradation products, or excipients in the formulation. rroij.com

For HPLC methods, specificity is often demonstrated by the separation of the analyte peak from other potential peaks. jpionline.org Peak purity analysis using a photodiode array (PDA) detector can confirm that the analyte peak is homogenous and not co-eluting with any impurities. rroij.comijnrd.org In one study, the peak purity values for the R and S diastereomers of this compound were found to be more than 99.00%, indicating no interference from degradants. rroij.com Similarly, another study reported peak purity values greater than 996, confirming the absence of interference. ijnrd.org For bioanalytical methods, specificity is established by demonstrating the absence of interfering peaks at the retention time of the analyte in blank matrix samples. jpionline.org

Linearity and Calibration Range

Linearity refers to the ability of an analytical method to elicit test results that are directly proportional to the concentration of the analyte in samples within a given range. ijcpa.in The calibration range is the interval between the upper and lower concentration of the analyte in the sample for which the analytical procedure has a suitable level of precision, accuracy, and linearity. ijcpa.in

For this compound, various analytical methods have established linearity over different concentration ranges. The correlation coefficient (r²), which should ideally be close to 1, is a measure of the goodness of fit of the calibration curve.

Table 2: Linearity and Calibration Range for this compound Analytical Methods

Precision (Repeatability and Intermediate Precision)

Precision expresses the closeness of agreement (degree of scatter) between a series of measurements obtained from multiple samplings of the same homogeneous sample under the prescribed conditions. ijcpa.inrroij.com It is usually expressed as the relative standard deviation (%RSD).

Repeatability (Intra-day precision) refers to the precision obtained under the same operating conditions over a short interval of time. rroij.com

Intermediate precision (Inter-day precision) expresses the variation within a laboratory, such as on different days, with different analysts, or with different equipment. rroij.com

According to ICH guidelines, the %RSD for precision should typically be not more than 2.0%. jpionline.org Numerous studies on this compound have demonstrated acceptable precision for the developed analytical methods.

Table 3: Precision Data for this compound Analytical Methods

Accuracy and Recovery Studies

Accuracy, in the context of analytical method validation, refers to the closeness of the test results obtained by the method to the true value. It is often determined through recovery studies by adding a known amount of the pure drug (analyte) to a placebo or a pre-analyzed sample and then analyzing the mixture. The percentage of the analyte recovered is then calculated.

Several studies have demonstrated the high accuracy of different analytical methods for this compound quantification. For instance, a Reverse Phase High-Performance Liquid Chromatography (RP-HPLC) method showed good recoveries at 60%, 100%, and 140% of the label claim, confirming its accuracy. rroij.com In another RP-HPLC method, the recovery rate for this compound was reported to be 99.43%. jpionline.org Recovery studies for this compound have consistently shown excellent results, with percentage recoveries often falling within the 98% to 102% range, indicating the methods are accurate and free from interference from excipients in the formulation. ejpmr.comzenodo.orgresearchgate.netakjournals.comjidps.com

Spectrophotometric methods have also been validated for their accuracy. Two methods, one based on the reduction of iron(III) to iron(II) and another involving the reduction of permanganate, demonstrated good accuracy with low relative errors. scielo.br

Below is a table summarizing the accuracy and recovery data from various studies:

Robustness and Ruggedness Assessments

Robustness and ruggedness are critical validation parameters that demonstrate the reliability of an analytical method during normal use. Robustness is the measure of a method's capacity to remain unaffected by small, but deliberate variations in method parameters. Ruggedness, on the other hand, is the degree of reproducibility of test results obtained by the analysis of the same samples under a variety of normal test conditions, such as different analysts, instruments, and laboratories.

The robustness of HPLC methods for this compound is typically evaluated by intentionally altering parameters like the mobile phase composition, flow rate, pH, and column temperature. rroij.comhumanjournals.com For example, in one study, the flow rate was changed by ±0.2 units from the standard 1.2 mL/min, and the column temperature was varied by ±2°C from 35°C. humanjournals.com The results showed that the assay value was only slightly affected, and system suitability parameters remained satisfactory, indicating the method's robustness. humanjournals.com Similarly, another study confirmed the robustness of their method by varying the mobile phase composition and flow rate, noting no significant changes in resolution and peak shapes. rroij.com

Ruggedness is often assessed by having different analysts, using different instruments, perform the analysis. humanjournals.com The relative standard deviation (RSD) of the results is then calculated. Low %RSD values indicate that the method is rugged. humanjournals.com Spectrophotometric methods have also been shown to be robust and rugged, with performance characteristics remaining largely independent of deliberate changes in experimental variables, analysts, and instruments. scielo.br

The following table presents findings from robustness assessments:

Limit of Detection (LOD) and Limit of Quantification (LOQ) Determinations

The Limit of Detection (LOD) and Limit of Quantification (LOQ) are important indicators of the sensitivity of an analytical method. The LOD is the lowest amount of an analyte in a sample that can be detected but not necessarily quantitated as an exact value. The LOQ is the lowest amount of an analyte in a sample that can be quantitatively determined with suitable precision and accuracy.

These limits are typically determined based on the standard deviation of the response and the slope of the calibration curve. For this compound, various analytical techniques have demonstrated a wide range of LOD and LOQ values, reflecting their differing sensitivities.

For instance, one RP-HPLC method reported an LOD of 50 ng/mL and an LOQ of 150 ng/mL. rroij.com Another RP-HPLC method showed even greater sensitivity with an LOD of 0.1 µg/mL and an LOQ of 0.3 µg/mL. jpionline.org A stability-indicating RP-HPLC method had an LOD of 0.52 μg/ml and an LOQ of 1.59 μg/ml. akjournals.com Spectrophotometric methods have also been developed with good sensitivity, with one study reporting LODs of 0.11 µg/mL and 0.21 µg/mL for two different methods (Method A and Method B, respectively). scielo.brusp.br

A summary of LOD and LOQ values for this compound using different analytical methods is provided in the table below:

Competition for Renal Tubular Secretion Pathways (e.g., with Probenecid)

Ganciclovir is primarily eliminated from the body by the kidneys through glomerular filtration and active tubular secretion. oatext.com Co-administration with drugs that also utilize this secretion pathway can lead to competitive inhibition, affecting the plasma concentration of ganciclovir.

Probenecid, a classic inhibitor of renal tubular secretion, demonstrates this interaction. When administered with oral ganciclovir, probenecid leads to a statistically significant decrease in the renal clearance of ganciclovir by 20%, resulting in a 40% increase in ganciclovir exposure. hpra.iemedsafe.govt.nzroche-hiv.comrowex.ie This interaction is consistent with competition for renal tubular excretion. hpra.iemedsafe.govt.nzroche-hiv.comrowex.ie Therefore, patients taking both probenecid and this compound should be monitored for potential ganciclovir toxicity. hpra.iemedsafe.govt.nzroche-hiv.comrowex.ie Other drugs that are eliminated via renal tubular secretion, such as pivmecillinam and temocillin, may also increase the levels of ganciclovir and vice versa. medscape.com

Interactions Affecting Plasma Concentrations of Co-administered Drugs (e.g., Didanosine, Mycophenolate Mofetil)

This compound, through its conversion to ganciclovir, can also influence the plasma concentrations of other co-administered drugs.

Didanosine: Plasma concentrations of didanosine have been consistently shown to increase when administered with ganciclovir (both intravenous and oral). medsafe.govt.nz With oral ganciclovir, the area under the curve (AUC) of didanosine increased by 84% to 124%. medsafe.govt.nz Similarly, with intravenous ganciclovir, the didanosine AUC increased by 38% to 67%. medsafe.govt.nz This pharmacokinetic interaction suggests that patients should be monitored for didanosine-related toxicities, such as pancreatitis. medsafe.govt.nzmpa.se Ganciclovir concentrations, however, were not significantly affected. medsafe.govt.nzmpa.se

Mycophenolate Mofetil (MMF): While a single-dose study in patients with normal renal function did not suggest a significant pharmacokinetic interaction between mycophenolic acid (MPA), the active metabolite of MMF, and ganciclovir, the potential for an interaction exists, particularly in patients with renal impairment. drugs.comhres.caeuropa.eu Both the glucuronide metabolite of MPA (MPAG) and ganciclovir are eliminated by the kidneys, and in the presence of renal impairment, they may compete for tubular secretion, potentially leading to increased concentrations of both drugs. drugs.comeuropa.eu Therefore, caution and monitoring are advised when co-administering this compound and MMF in patients with impaired renal function. drugs.comeuropa.eu

Mechanistic Studies on Interactions with Myelosuppressive Agents at a Molecular Level

The co-administration of this compound with other myelosuppressive agents can lead to additive toxicity. roche-hiv.comrowex.ie This is a pharmacodynamic interaction rather than a pharmacokinetic one, as both types of drugs can suppress bone marrow function. rowex.ie

Drugs known to be myelosuppressive include zidovudine, dapsone, pentamidine, flucytosine, vincristine, vinblastine, doxorubicin, and hydroxyurea. roche-hiv.com For instance, both zidovudine and ganciclovir have the potential to cause neutropenia and anemia. medsafe.govt.nzrowex.ie The concurrent use of these agents can result in severe hematological toxicity. nih.gov The toxicity of ganciclovir may also be enhanced when co-administered with drugs that can cause renal impairment, as this can reduce the clearance of ganciclovir and increase its exposure. roche-hiv.com

Assessment of Inhibitory Concentrations (IC50) in In Vitro Viral Replication Assays

The in vitro antiviral activity of ganciclovir against cytomegalovirus (CMV) is measured by its 50% inhibitory concentration (IC50). The IC50 for ganciclovir against clinical and laboratory isolates of human CMV has been reported to range from 0.08 to 22.94 µM (0.02 to 5.75 µg/mL). fda.gov Other sources report a similar range of 0.08 µM (0.02 µg/mL) to 14.32 µM (3.58 µg/mL). medsafe.govt.nz A mean IC50 of 0.7 mg/L (approximately 2.8 µM) has also been noted among CMV clinical strains. nih.gov

Differential Targets of Newer Antivirals (e.g., Maribavir's pUL97 inhibition, Letermovir's terminase complex inhibition)

Newer antiviral agents have been developed with different mechanisms of action compared to ganciclovir, offering alternatives for the management of CMV, particularly in cases of resistance.

Interactions with Cellular Guanylate Kinase and Other Host Kinases

The conversion of ganciclovir monophosphate to its diphosphate form is a critical step mediated by the host cell enzyme guanylate kinase (GUK1). pharmgkb.orgnih.govwikipedia.org Subsequently, a variety of cellular kinases are responsible for the final phosphorylation to the active triphosphate form. pharmgkb.orgnih.govwikipedia.org These kinases are typically involved in the physiological production of guanosine triphosphate (GTP) and deoxyguanosine triphosphate (dGTP). pharmgkb.org

Identified host kinases involved in the formation of ganciclovir triphosphate include:

Phosphoglycerate kinase pharmgkb.orgnih.govwikipedia.org

Pyruvate kinase pharmgkb.org

Phosphoenolpyruvate carboxykinase pharmgkb.org

Nucleoside diphosphate kinase pharmgkb.orgnih.gov

Succinyl-CoA synthetase pharmgkb.org

Creatine kinase pharmgkb.org

Adenylosuccinate synthetase pharmgkb.org

This reliance on a cascade of host cell enzymes for full activation underscores the intricate interplay between the antiviral agent and the host's cellular machinery. The efficiency of these enzymatic conversions can influence the intracellular concentration of the active GCV-TP, which is a key determinant of its antiviral efficacy. The accumulation of GCV-TP is notably higher in CMV-infected cells, contributing to the drug's selective activity. nih.govwikipedia.org

Assessment of Human DNA Polymerase Affinity and Inhibition Profile

The primary mechanism of action of ganciclovir triphosphate is the inhibition of viral DNA polymerase. nih.govwikipedia.orgoup.com However, its interaction with human (host) DNA polymerases is also a critical factor, as this interaction is linked to potential host cell toxicity.

Research indicates that ganciclovir triphosphate is a selective inhibitor, demonstrating a significantly weaker inhibition of cellular DNA polymerases compared to the viral DNA polymerase. nih.govwikipedia.org This selectivity is a cornerstone of its therapeutic window. While GCV-TP acts as a competitive inhibitor of deoxyguanosine triphosphate (dGTP) incorporation into the growing DNA chain by viral DNA polymerase, its affinity for human DNA polymerases is considerably lower. patsnap.com

Studies have shown that ganciclovir inhibits viral DNA polymerases more effectively than cellular polymerases. drugbank.comdrugbank.com The incorporation of ganciclovir triphosphate into the DNA strand by viral DNA polymerase leads to the slowing of DNA replication. oup.com In contrast, its effect on cellular DNA polymerases is less pronounced. nih.govwikipedia.org

Table 1: Comparative Inhibition of Viral vs. Human DNA Polymerases by Ganciclovir Triphosphate

This differential inhibition profile is fundamental to the clinical utility of this compound, allowing for the suppression of viral replication with a manageable impact on host cell DNA synthesis.